This invention pertains to electric motors and actuators. More particularly, this invention relates to unitary electric motor and actuator assemblies having explosion-proof construction that facilitates use in explosive gas environments.
The construction and utilization of linear and rotary actuators is well understood. For example, electro-mechanical actuators have included hydraulic actuators, pneumatic actuators, and ball-screw actuators. For various reasons discussed below, none of the prior art linear actuators are suitable for use in applications where there is a potentially explosive environment, and where there is limited package space. For example, none of the prior art devices are suitable for driving a fuel and air delivery valve for a gas turbine engine where there is limited package space, and the actuator requires precision actuation within a potentially explosive environment. It is believed that other similar applications exist where there is a need for a limited package space actuator that can operate within a potentially explosive environment.
Hydraulic linear actuators are well known in the art. Typically, a hydraulic actuator is actuated via an arrangement of hydraulic valves to impart axial movement of an actuator rod. The actuator rod is used to impart movement to a mechanical component such as a kinematic linkage on a machine. However, the ability to precisely control movement is somewhat limited to the ability to accurately control fluid flow via the hydraulic valves. Furthermore, hydraulic fluid tends to leak from the actuator, particularly over time as seals within the actuator wear during use. Even furthermore, the hydraulic actuator and control valves are provided as separate components which tends to prevent use where package space is limited.
Pneumatic linear actuators are also well known in the art. Typically, a pneumatic actuator is actuated via a supply of pressurized gas via a pneumatic valve assembly. Similar to a hydraulic actuator, the pneumatic actuator has a rod that imparts movement to a mechanical component. Also similar to the hydraulic actuator, the pneumatic actuator and pneumatic valve assembly are provided as separate components which tends to prevent use where package space is limited.
Rotary threaded shaft actuators are additionally well known in the art. Examples of such actuators include ball screw actuators, and improvements on such actuators that use some form of modified nut and threaded shaft to generate linear actuation. Examples includes U.S. Pat. Nos. 3,965,761 and 4,496,865, herein incorporated by reference. A rotary motor generates rotational motion that is converted into linear motion with the aid of a linear traveling device such as a threaded shaft cooperating with a threaded nut assembly. However, an electric motor having a permanent magnetic field is used to drive these threaded shaft actuators. Use of such electric motors tends to be somewhat imprecise for applications that require precise axial movement, such as is used when metering fuel and air delivery via a valve assembly for a turbine engine. Furthermore, such electric motors are typically DC motors that include motor brushes. However, such brushes are known to generate sparks which can be hazardous when using the actuator within a potentially explosive environment.
Recent advances have been made in the field of brushless DC motors. However, such motors require the use of a computer controller in order to precisely control operation of the brushless motors, and such computer controllers increase the packaging size and complexity. Additionally, the control electronics are typically provided on one or more printed circuit boards which provide an additional source for generating a spark that could prove dangerous when used in a potentially explosive environment. Furthermore, these motors have only been provided in housings that are separate from a linear actuator that is driven by the motor. Hence, the package space is relatively bulky.
Accordingly, there exists a need for a motorized actuator that is compact and suitable for use in potentially explosive environments, such as for operating fuel and air delivery valves for gas turbine engines.
A rugged explosion-proof actuator is provided with onboard electronics and a precise brushless DC motor. Explosion-proof functionality is imparted via one or more gas exit paths designed to impart explosion-proof flame paths within a single, relatively compact and unitary actuator and motor housing. According to one construction, the actuator is a linear actuator. According to another construction, the actuator is a rotary actuator.
According to one aspect of the invention, an actuator assembly includes an explosion-proof housing, a motor and an actuator. The housing has an inner cavity. The motor is disposed within the housing. The actuator is carried by the housing and communicates with the motor. The actuator is operative to generate movement externally of the housing responsive to actuation of the motor.
According to another aspect of the invention, an actuator assembly includes a housing, a motor, motor control electronics, and an actuator. The housing has an inner cavity. The motor is disposed within the housing. The motor control electronics communicate with the motor and are disposed within the housing. The actuator is carried by the housing and communicates with the motor. The actuator is carried for movement relative to the housing responsive to actuation of the motor.
According to yet another aspect of the invention, an explosion-proof actuator assembly includes an explosion-proof housing, a motor, motor control electronics, and an actuator. The housing has at least one inner cavity and at least one exit path comprising an explosion-proof flame path. The motor is disposed within the housing. The motor control electronics communicate with the motor and are disposed within the housing. The actuator is carried by the housing, communicates with the motor, and is operative to generate movement externally of the housing responsive to actuation of the motor.